<style>
button{
  width:100px;
  height:40px;
  margin:10px;
  font-size:30px;
  color:red;
}
</style>
<script>
  var i = 65;
  for(i=65;i<=65+25;i++){
  document.write("<button>"+String.fromCharCode(i)+"</button>");
  
}
</script>